1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition. More particularly, the present invention relates to a radiation-sensitive resin composition suitable as a resist for ultra-microprocessing utilizing various types of radiation such as ultraviolet radiation, deep ultraviolet radiation, X-rays, and charged particle rays.
2. Description of Background Art
In the field of microprocessing represented by the production of integrated circuit elements, lithographic technology capable of performing microprocessing of sub half-micron order or less with good reproducibility has been developed in order to increase integration of the integrated circuits.
In a conventional lithographic process, a positive-tone resist using an alkali-soluble resin such as a novolac resin and a quinonediazido photosensitizer is typically used as a resist. A negative-tone resist is also known as such a resist. Since performance of these types of resists has almost reached a limit, it is difficult to use these resists in microprocessing of a sub half-micron order or less. In a conventional lithographic process utilizing ultraviolet radiation such as g-rays(wavelength: 436nm) and i-rays (wavelength: 365nm) from a mercury lamp, sufficient theoretical depth of focus cannot be achieved in the case of forming a minute pattern of 0.35 .mu.m or less by using the above positive-tone resist.
Therefore, a lithographic process utilizing deep ultraviolet radiation, X-rays, or charged particles rays capable of achieving a wider range of depth of focus has been studied in order to produce a minute pattern of 0.35 .mu.m or less.
However, conventional resists have problems related to pattern shape, sensitivity, contrast, developability, and the like, when using deep ultraviolet radiation, X-rays, or charged particle rays. In the case of deep ultraviolet radiation, the shape of the pattern produced using a negative-tone resist tends to become an "inverted tapered-shape", in which the bottom of the pattern is thinner than the top, due to too great light absorption of the resist. The resist pattern produced using a positive-tone resist also becomes a tapered-shape, in which the bottom of the pattern is thicker than the top. Therefore, it is difficult to form a rectangular pattern in both cases.
Moreover, sensitivity, contrast, and the like are inadequate. In the case of using radiation having higher energy such as X-rays or charged particle rays, decrease in the sensitivity is more significant than in the case of using deep ultraviolet radiation. In particular, a positive-tone resist of which the solubility in a developer should otherwise increase upon irradiation of an energy ray, becomes less soluble when irradiated by such a higher energy radiation.
In view of the above situation, a chemically-amplified resist comprising a photoacid generator (a compound which generates acid upon irradiation) has attracted attention as an advanced resist. The chemically-amplified resist has excellent sensitivity to various types of radiation by the catalytic action of acid generated.
As such a chemically-amplified resist exhibiting comparatively good resist performance, a resist comprising a resin having a t-butyl ester group or a t-butoxycarbonyl group (for example, Japanese Patent Publication No. 27660/1990), a resist comprising a resin having a silyl group (for example, Japanese Patent Publication No. 44290/1991), a resist comprising a resin having an acrylic acid component (for example, Japanese Patent Application Laid-open No. 39665/1992), and the like are known. However, these chemically-amplified resists have their own peculiar problems and various difficulties in practical application. One of the problems which has recently been pointed out is a round edge of the top portion which is produced during microprocessing of a thin film with a design dimension of about 0.20 .mu.m.
As a radiation-sensitive resin composition for chemically-amplified resists, Japanese Patent Application Laid-open No. 127700/1997 discloses a composition comprising a water-insoluble organic polymer binder, such as a 4-hydroxystyrene/4-tetrahydropyranyloxystyrene copolymer, which comprises an acid unstable group and becomes soluble in an alkali aqueous solution by the action of an acid, and a quaternary ammonium salt compound such as quaternary ammonium organic acid salt as a composition exhibiting improved photosensitivity, processing characteristics, and contrast. Moreover, Japanese Patent Application Laid-open No. 179303/1997 discloses that the photo speed can be controlled by the use of a composition comprising a resin binder such as a hydroxystyrene/t-butyl (meth)acrylate copolymer which comprises an acid unstable group and a quaternary ammonium salt compound such as quaternary ammonium hydroxyalkanoyl. In particular, Japanese Patent Application Laid-open No. 179303/1997 discloses that superior performance can be obtained by using hydroxy-substituted alkanoyl as the counter ion of the quaternary ammonium salt compound, in comparison with the case of using alkanoyl without hydroxy-substitution.
However, these compositions are still inadequate from the viewpoint of preventing the top edge of the pattern from rounding, which is the big problem in microprocessing of design dimensions of about 0.20 .mu.m with a thin film.
Therefore, development of a chemically-amplified resist exhibiting excellent sensitivity and resolution capable of preventing the top edge of the pattern from rounding in microprocessing with a thin film is strongly demanded.
An object of the present invention is to provide a radiation-sensitive resin composition capable of producing a rectangular resist pattern while preventing the top edge of the pattern from rounding, which is a big problem in microprocessing of design dimensions of about 0.20 .mu.m with a thin film of, for example, 0.6 .mu.m or less.
Another object of the present invention is to provide a radiation-sensitive resin composition which is highly sensitive to deep ultraviolet radiation, X-rays, and charged particle rays, and exhibits excellent sensitivity, resolution, and the like.